Expandable polystyrene compositions



United States Patent 3,259,595 EXPANDABLE POLYSTYRENE COMPOSITIONS Harold A. Wright, Murrysville, Pa., assignor to Koppers Company, Inc., a corporation of Delaware No Drawing. Filed July 15, 1963, Ser. No. 295,197 6 Claims. (Cl. 2602.5)

This invention relates generally to expandable styrene polymers. It pertains particularly to expandable copolymer compositions comprising lightly cross-linked expandable polystyrene.

Expandable styrene polymers which expand to 560 times their original dimensions when subjected to heat have been made heretofore by incorporating from 5-15 percent by weight of a suitable expanding agent, e.g., an aliphatic hydrocarbon, in the polymer. When such particles of expand-able polystyrene are heated under confinement, the particles expand and fuse together to produce a plastic foam having a closed cellular structure. Such expandable polymers are commercially available. DAlelio, US. Patent No. 2,983,692 which issued May 9, 1961, for example, describes a method of producing expandable polymers.

The unique versatility of expandable styrene polymers has been successfully demonstrated in many different fields. Expandable styrene polymers have, for example, been used for low-temperature insulation, for packaging, in containers for hot or cold beverages, in flotation equipment, and in housing construction.

It has been recognized, nevertheless, that even greater use and advantage could be made of expandable styrene polymers if the expandable styrene polymers had relatively low densities, uniformly, small cell sizes and improved thermal resistance. The diameter of the cells of heretofore knovm foamable styrene polymers may vary, in the same foamable particle, from 650 mils. These styrene polymers or molded articles made therefrom are also subject to collapse and excessive shrinkage during foaming or heating operations whenever a foaming temperature of 100 C. (in excess of the incipient softening point of the styrene polymer) or greater is applied thereto.

The disadvantageous non-uniform, large celled, and low thermal resisting characteristics of the expandable polystyrene foams are particularly critical inthe manufacture of insulated cups and other thin-walled molding materials. Large cells, particularly on the surface of the molded materials, present a distinctly, disadvantageous aesthetic quality to the molded materials because of the frosty or crystal appearance (as opposed to opaque, white) and they also impair fusion which in the case of insulated cups contributes to undesirable leaking problems. Low thermal resistant properties foster shrinkage of the individual expanded beads or molded articles when they are exposed to exaggerated heating conditions. For example, conduction-type heating, as is frequently used in thin-wall molding, imposes particular difiiculties in this area; a burned, shrivelled exterior being common when higher temperatures and/or longer heating cycles are used in order to get adequate fusion among the polymeric particles.

It is also well-known that if expandable polystyrene particles can produce foam structures of low density, e.g., about one pound per cubic foot, the thus-produced foamed materials will be advantageous when they are used as insulation, fillers, lightweight aggregate, etc. Low density, uniformly small-celled, expandable polystyrene has heretofore been produced, for example, by incorporating an isopentane paraffinic hydrocarbon additive blowing agent into the styrene polymer. The required use of the isopentane-paraffin blowing agent in expandable polyice styrene has provided disagreeable odors within the expanded articles manufactured therefrom. These odors are particularly undesirable when the expandable particles are used to manufacture such products as drinking cups.

This invention provides a novel, expandable copolymer composition which will yield foamable particles that, upon foaming, will expand to about one pound per cubic foot densities, retain uniform cell sizes of from two to twelve mils, and be thermally resistant to temperatures greater than C. The novel expandable copolymer of this invention is comprised of a predominant amount of styrene and a minor proportion of a diallyl ester of an unsaturated aliphatic dibasic acid which acid contains from four to five carbon atoms, said copolymer having incorporated therein a normally liquid expanding agent.

Styrene polymers, as referred to in the compositions of this invention, include corresponding polymers of closely related homologues, e.g., alpha-methyl styrene; ortho, meta, and para-ethyl styrene; ortho, meta, and para-methyl styrene; 2,4-dimethyl styrene, etc.

The diallyl esters of unsaturated aliphatic dibasic acids useable in this invention include diallyl fumarate, diallyl itaconate, and the like.

In accordance with this invention, expandable copolymer particle-s capable of being expanded into low density, uniformly small-celled, thermally resistant cellular polymeric structures are produced by polymerizing a solution, in a suspension polymerization system, of styrene and a diallyl ester of an unsaturated aliphatic dibasic acid and thereafter subjecting the suspension of copolymer to an atmosphere of a normally liquid expanding agent boiling within the range 25-40 C., e.g., normal pentane. The expanding agent may, of course, be incorporated into the expandable copolymer in any of other well-known ways. For example, the styrene-diallyl ester copolymer may be fed through an extruder and the expanding agent injected into the extruder so as to be incorporated into a molten mass of styrene diallyl ester copolymer. Thereafter the novel copolymer particles containing an expanding agent can be individually expanded to provide discrete cellular particles having low densities (about 1 lb./ft. uniformly small cells, and good thermal resistivity. These individually expanded particles can then be placed in a mold and heated at a temperature above the boiling point of the expanding agent and above the softening or heat distortion temperature of the novel copolymer. Because of the exceptional expandable properties of the novel copolymer particles of this invention, an integral cellular copolymeric structure having low density, uniformly small cell sizes, and good thermal resistant chmacterist-ics can be produced.

Advantageously, the diallyl esters are used, in preparing this copolymer, to the extent of from 0.20.4 percent by weight based on the Weight of the total monomers. Expandable copolymers of styrene and a diallyl ester containing less than 0.2 percent of the ester do no provide copolymer foams of high thermal resistance and .as a result, these foams are subject to collapse or shrinkage upon heating at foaming temperatures of from mil- C. Expandable copolymers containing more than about 0.4 percent by weight of the diallyl ester become too highly cross-linked and, as a result, resist expansion by the pentane expanding agent and therefore can not provide low density, uniformly small-celled products.

The pentane which is used advantageously as the expanding agent for the novel copolymer of this invention may be a commercial grade of normal pentane which boils in the range of 3-()36 C.

The invention will be illustrated further by the following examples.

Patented July 5, 1966 3 Example I To a kettle equipped with a stirrer, 500 grams of deionized water are admixed with 0.015 gram Nacconol- NRSF (sodium dodecylbenzenesulfonate), 6 grams of hydroxyapatite and the system purged with nitrogen. There are then added 500 grams of styrene containing 1 gram of benzoyl peroxide and 0.25 gram of t-butyl perbenzoa-te and simultaneously there are added 1.25 grams of diallyl itaconate and stirring is commenced. The system is heated over a period of from 7 to 9 hours at 90 C. and thereafter the mass is heated at 115 C. for four hours. The mass is then cooled to room temperature and then there are added 3.0 grams of Nacconol and 75.0 milliliters of n-pentane and the system maintained at 90 C. at approximately 60-90 p.s.i. for eight hours. The suspension is cooled, the beads separated therefrom by centrifuging and the beads washed with dilute hydrochloric acid and then water washed. There are obtained freefiowing expandable copolymer beads containing pen tane.

Dried expandable copolymer particles made as above may be heated immediately after manufacture using conventional means such as described on page 19 of the Koppers Company, Inc. booklet entitled Dylite Expandexperiments in this example were subjected also to the physical tests performed on the expandable copolymer particles obtained in Example I. Table II identifies each expandable copolymer composition by stating the proportions of styrene and diallyl ester monomer starting materials from which the copolymers were prepared. Table II also gives the thermal stability of the foam expressed in terms of collapsibility after heating at a foaming temperature greater than 150 C. for a period of two hours. The cell-size measurement of the expanded foams was evaluated nn'croscopically using a projected stage micrometer scale to measure the approximate cell diameters. To this end, an expanded bead was sliced into two hemispheres and a wedge-like semicircular wafer whose straight edge forms the apex of the wedge was cut from the one hemisphere. This wafer was used under 50x magnification, the image being superimposed on the projected scale above to permit direct measurement of the various cells along the base of the semicircle. By having the apex of the wedge coincide with this base, interference from shadows of all the cells behind the one being measured was avoided. The range of values recorded in Table II represents the majority of cells along the base.

TABLE II Weight Foam Foam Monomers Percent Behavior in Toluene Thermal Stability Density Cell Size (lb./ft. (mils) St ren 99.80 1 gil f 20 }Smooth Solution Rating No. 2.. 1. 05 5-10 tyrene 99.75 n 2 {lsDiallyl Itaoonate. 0. Ratmb 3 02 44;

tyrene 99. 75 a ]S3iany1Fumame 25 do Rating Nos. 3-4 1. 22 6-12 tyrene 99. 70 4 I Dian l Itac01'1ate 0. Rafmg 4 08 3-3 tyrcne 99. 5 {manyutaconatenu 0.35 }Somewhat Viscous Solution do 1.14 5-10 }Viscous Solution Rating Nos. 4-5 1. 22 6-12 Smooth Solution Rating No. 1 1.05 6-46 able Polystyrene to make low density foam materials, i.e., having a density of about one pound per cubic foot having uniformly small cell sizes and being resistant to temperatures of between 150 C.

The expanded copolymer particles prepared in accordance with the procedure of Example I were subjected to varying behavior tests to determine cell size, density, thermal resistance, and behavior toward toluene. The results of these tests are noted below in Table I.

For purpose of comparison a composition of expandable polystyrene was prepared and foamed under similar conditions. The results of thermal stability, cell size, density and behavior in toluene tests are also included in the Table II.

Example III In each of a series of experiments a charge of styrene and a diallyl ester of an unsaturated aliphatic dibasic TABLE I Foam Foam Cell Starting Comonomcrs Weight Behavior in Thermal Stability 2 Density Slzc Percent Toluene 1 (lb./ft. A(ve rage mi s Styrene 99. 75 1 {many1 Itaconate 0. 25 }Smooth Solution Partial Collapse, Rating No. 3 1.02 46 1 Appearance of 0.5 gram of impregnated beads in 5 ml. of toluene rolled in a capped vial for 24 hours at room temperature. 2 Appearance of one gram of impregnated beads after heating at C. for two hours.

3 Rated on the basis:

Description:

Totally collapsed button Partially collapsed, no strings Partially collapsed, stringy Little collapse, stringy" Little collapse, no string No collapse Example II In each of a series of experiments, copolymer expandable foams were prepared in accordance with the procedure of Example I. The copolymer foams were prepared using, as the monomeric starting materials, styrene and esters of dibasic acids. The proportions of monomers used in preparing the copolymers were varied within the ranges specified hereinabove. The various expandable copolymer materals prepared in the series of Rating TABLE III Weight Foam Foam Monomers Percent Behavior in Toluene Thermal Stability Density Cell Size (lbJttfi) (mils) Styrene 99. 95 6-24 1 {g ltaconateflu g }Smo0th Solution Rating No. 1 0. 97 6-16 tyrene 99. 5 2 {Diallyl Itaconate 0.15 Rating 1 2 }Swollen, Sticky Beads Rating No. 5 1. 3e }Swolleu, Free Flowing Beads. Rating N o. 6 1. 67 [Styrene 99. 50 6-12 5 lDiauyl Fumamte 5o }Swollen, Sticky Beads Ratmg Nos. 545 1.53

In the above examples and their resultant tables, the test which indicates the behavior of the polymers and the copolymers toward toluene is significant in determining the abiilty of the particular expandable copolymers to provide low, e.g., about one pound per cubic foot density copolymer foams having uniformly small cell size. In observing the action of toluene on the particular materials an expandable foam which forms smooth solution or slight gel in the toluene will upon expansion under heat provide desirable low density foam materials. On the other hand, those copolymers which, when observed in toluene, provide thick viscous gels or become swollen beads do not provide the required low density foam products. In fact, the density becomes extremely high and undesirable. This is an indication of the amount or the degree of cross-linking which takes place between the copolymers. The range amount of esters used in preparing the copolymer foams of this invention is therefore extremely critical with respect to the ulti-' mate density, as well as cell size, of the foamed products.

Polystyrene foams, as opposed to the copolymer foams of this invention, do not have good thermal stability and uniformly small cell sizes even though the polystyrene foams form a smooth solution in toluene. It is only those copolymer foams as provided in this invention, which contain the critical coomonomer amounts and which form solutions in toluene, that have good thermal stability, uniformly small cell sizes, and low densities.

In each of the examples wherein comparative data is given between copolymer foams and polymer foams, e.g., expandable polystyrene, the conditions of polymerization, impregnation with expanding agent, and retention of volatiles was kept substantially identical.

The foregoing has described a novel, foamable copolymer particle and a method for producing said particle. The novel foamable copolymer of this invention will expand to densities of about one pound per cubic foot. The thus-expanded particles or beads also contain uniformly small cells which measure from two to twelve mils in diameter. The expandable copolymer particles can be placed in a mold and subjected to intensive heat which heat is in excess of that applicable to normal expandable styrene polymers to cause them to expand and fuse together into a fused shaped foamed object. The shaped foamed object made from the novel copolymers of this invention will advantageously not shrink during the application of heat in the range of 100-l50 C. The shaped foamed objects will retain substantially the same density as the expandable particles from which the shaped object is made and the individual foam particles making up the foamed object will also have substantially uniform cells averaging from two to twelve mils in diameter.

The foamed products made from these novel particles are useful as insulated building panels, floats, cushioning materials, contains for hot or cold liquids, display objects and the like. The ability to expand to low density in a given volume makes the use of the particles economically advantageous for all applications where lightweight foamed objects are of interest.

I claim:

1. A foamable styrene copolymer suitable for forming a cellular article possessing uniformly small cells, good thermal stability at temperatures between IOU- C. and having a density of about one pound per cubic foot which composition comprises a copolymer of from 99.6-99.8 parts by weight of styrene and from 0.4-0.2 part by weight of a diallyl ester of an unsaturated aliphatic dibasic acid which acid contains from four to five carbon atoms selected from the group consisting of diallyl itaconate and diallyl fumarate, said copolymer being soluble in toluene and, said copolymer having uniformly incorporated therein a normally liquid expanding agent.

2. An expandable copolymer composition comprising a copolymer of from 99.6-99.8 parts by weight of styrene and from O.40.2 part by weight of a diallyl ester of an unsaturated aliphatic dibasic acid which acid contains from four to five carbon atoms selected from the group consisting of diallyl itaconate and diallyl fumarate, said copolymer being soluble in toluene, and said copolymer having uniformly incorporated therein a normally liquid expanding agent.

3. A foamable copolymeric particle having uniformly incorporated therein a normally liquid expanding agent, said copolymeric particle being comprised of styrene and from 0.4-0.2 part by weight of a diallyl ester of an unsaturated aliphatic dibasic acid selected from the group consisting of diallyl itaconate and diallyl fumarate which acid contains from four to five carbon atoms, and said copolymer being soluble in toluene.

4. The composition of claim 1 in which said normally liquid expanding agent is pentane.

5. A method for the production of lightly cross-linked foamable styrene copolymerie particles which upon heating will expand to a structure of about one pound per cubic foot density having unifonnly small cells and improved thermal stability which method comprises forming an aqueous suspension of a peroxide catalyst, from 99.6-99.8 parts by weight of styrene, from (1.4-0.2 part by weight of a diallyl ester of an unsaturated aliphatic dibasic acid selected from the group consisting of diallyl itaconate and diallyl fumarate with the aid of a suspending agent, heating said suspension to cause said styrene and said acid to copolymerize to form a suspension of particles of copolymer, said particles being insoluble in toluene contacting said suspension with a normally liquid expanding agent until said expanding agent is incorporated within said particles and thereafter separating said partiles from said medium.

diallyl itaconate.

References Cited by the Examiner FOREIGN PATENTS 632,108 11/1949 Great Britain.

OTHER REFERENCES UNITED STATES PATENTS 5 Styrene, Its Polymers, Cop o1y mers and Derivatives, 2x213 erm--1111; 225532;: 55 3 51:22; E ZiiLi?if 22322;; SAMUEL 8/ 1958 Rubens 26()--2,5 10 MURRAY TILLMAN, Examiner.

35132? ELZEEZMZ'IZZIZZZ $325.? FOELAK 

1. A FOAMABLE STYRENE COPOLYMER SUITABLE FOR FORMING A CELLULAR ARTICLE POSSESSING UNIFORMLY SMALL CELLS, GOOD THERMAL STABILITY AT TEMPERATURES BETWEEN 100-150* 4C. AND HAVING A DENSITY OF ABOUT ONE POUND PER CUBIC FOOT WHICH COMPOSITION COMPRISES A COPOLYMER OF FROM 99.6-99.8 PARTS BY WEIGHT OF STYRENE AND FROM 0.4-0.2 PART BY WEIGHT OF A DIALLYL ESTER OF AN UNSATURATED ALIPHATIC DIBASIC ACID WHICH ACID CONTAINS FROM FOUR TO FIVE CARBON ATOMS SELECTED FROM THE GROUP CONSISTING OF DIALLYL ITACONATE AND DIALLYL FUMARATE, SAID COPOLYMER BEING SOLUBLE IN TOLUENE AND, SAID COPOLYMER HAVE UNIFORMLY INCORPORATED THEREIN A NORMALLY LIQUID EXPANDING AGENT. 